Modular prosthetic component with improved body shape

ABSTRACT

An improved body element for use in a modular prosthetic stem component of the sort comprising a body element and at least one other element, wherein the body element and the at least one other element are joined together by at least one modular connection, wherein the improved body element comprises an anterior wall and a posterior wall, at least one of the anterior wall and the posterior wall converging toward the other on the medial side of the body element and diverging away from the other on the lateral side of the body element, whereby the body element approximates a general wedge shape.

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This is a continuation of pending prior U.S. patent application Ser. No.09/960,175, filed Sep. 20, 2001 by Daniel E. E. Hayes, Jr. et al. forMODULAR PROSTHETIC COMPONENT WITH IMPROVED BODY SHAPE, now U.S. Pat. No.6,843,806, issued Jan. 18, 2005, which in turn claims benefit of priorU.S. Provisional Patent Application Ser. No. 60/233,875, filed Sep. 20,2000 by Daniel E. E. Hayes, Jr. et al. for MODULAR PROSTHETIC IMPLANT.The above-identified patent and patent application are herebyincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to surgical apparatus and procedures in general,and more particularly to orthopedic prostheses for restoring a joint.

BACKGROUND OF THE INVENTION

Joint replacement surgery seeks to replace portions of a joint withprosthetic components so as to provide long-lasting function andpain-free mobility.

For example, in the case of a prosthetic total hip joint, the head ofthe femur is replaced with a prosthetic femoral stem component, and thesocket of the acetebulum is replaced by a prosthetic acetabular cupcomponent, whereby to provide a prosthetic total hip joint.

In the case of a prosthetic total knee joint, the top of the tibia isreplaced by a prosthetic tibial component, and the bottom of the femuris replaced by a prosthetic femoral component, whereby to provide aprosthetic total knee joint.

Still other prosthetic total joints, and their constituent components,are well known in the art.

The present invention is directed to orthopedic prostheses for restoringthe hip joint and, more particularly, to improved prosthetic femoralstem components.

Prosthetic femoral stem components typically comprise a proximal sectionfor seating in the proximal section of the resected femur and presentinga ball for seating in the acetabular socket, and a distal section forseating in the femur's medullary canal so as to extend along the shaftof the femur.

It is, of course, important that the prosthetic femoral stem componentmake a proper fit with the surrounding bone. To this end, prostheticfemoral stem components are typically offered in a range of differentsizes in an effort to accommodate variations in patient anatomy.However, despite this, it has been found that it can be difficult toprovide the correct prosthetic femoral stem component for patients. Thisis due to the wide variation in patient anatomies and the practicallimitations of hospital inventory. By way of example, where a femoralcomponent is selected having a proximal section appropriately sized forthe proximal section of the resected femur, the distal section of theprosthesis may not be appropriately sized for proper seating in thedistal section of the femur. This can present serious problems for thepatient, including problems relating to joint stability and pain.

On account of the foregoing, there has been substantial interest informing prosthetic femoral stem components out of a plurality ofseparate elements, wherein each of the elements may be independentlyselected so as to most closely approximate patient anatomy, and whereinthe separate elements may be assembled to one another in the operatingroom, using modular connections, so as to provide the best possibleprosthetic femoral stem component for the patient.

Modular prosthetic femoral stem components are offered in a variety ofconfigurations.

By way of example, a so-called “two part” modular prosthetic femoralstem component may comprise a body element and a combined neck-and-stemelement. More specifically, the body element includes a central aperturethrough which the combined neck-and-stem element extends. The bodyelement is selected so that its outer surface is appropriately sized forproper seating in the proximal section of a resected femur. The combinedneck-and-stem element is selected so that when it is mounted to the bodyelement and deployed within the femur, a ball located at the proximalend of the combined neck-and-stem element will be properly seated in thehip joint's corresponding acetabular cup while the distal end of thecombined neck-and-stem element will be properly seated within themedullary canal of the femur. The body element and the combinedneck-and-stem element are adapted to be secured to one another in theoperating room, using modular connections, so as to form the completemodular prosthetic femoral stem component. Such modular connections arewell known in the art.

Other types of “two part” modular prosthetic femoral stem components arealso well known in the art.

By way of further example, a so-called “three part” modular prostheticfemoral stem component may comprise a body element, a neck element and astem element. More specifically, the body element includes a centralaperture into which portions of the neck element and the stem elementextend. The body element is selected so that its outer surface isappropriately sized for proper seating in the proximal section of aresected femur. The neck element is selected so that when it is mountedto the remainder of the modular prosthetic femoral stem component anddeployed within the femur, a ball located at the proximal end of theneck element will be properly seated in the hip joint's correspondingacetabular cup. The stem element is selected so that its outer surfaceis appropriately sized for proper seating within the medullary canal ofthe femur. The body element, the neck element and the stem element areadapted to be secured to one another in the operating room, usingmodular connections, so as to form the complete modular prostheticfemoral stem component. Again, such modular connections are well knownin the art.

Other types of “three part” modular prosthetic femoral stem componentsare also well known in the art.

Thus it will be seen that the modular prosthetic femoral stem componentgenerally comprises: (1) a motion structure that reproduces the motionof the original, natural joint; and (2) a load structure that transmitsthe loads caused by that motion (e.g., walking) to the remaining bone ofthe resected femur. The motion structure generally comprises the neck(and ball) portion of the modular prosthetic femoral stem component. Theload structure generally comprises two portions: a body portion for thetransmission of axial and torsional loads to the remaining bone of theresected femur, and a stem portion to assist the body portion inresisting bending loads placed upon the body portion. In this context,the body portion is the aforementioned body element of theaforementioned “two part” modular prosthetic femoral stem component andthe aforementioned body element of the aforementioned “three part”modular prosthetic femoral stem component.

The goal of the body element of a modular prosthetic femoral stemcomponent is to transmit loads to the remaining bone of the resectedfemur in the same regions that the bone originally carried those loads.At the ends of the bone, this is indicated by the areas of greatestcortical bone thickness or cancellous bone density. Bone grows inresponse to mechanical stress. Where bone is needed to resist load, itforms; where it is not needed to resist load, it is resorbed. Thisprinciple is known as Wolff's Law. The loads generated by joint motionare preferentially carried by the bone at the end nearest the joint. Ifa prosthesis bypasses this region in favor of loading the more centralsection of the bone, resorption at the end of the bone will result. Thiscan eventually lead to fracture of the bone or loosening of theprosthesis.

Thus, in order to transfer loads to the correct region of the bone, andto transfer the loads uniformly in that region, the body element of theprosthesis should, ideally, closely but not exactly approximate theinner contour of the hard cortical bone. More particularly, it has beenfound that it is preferable to leave a small amount of compactedcancellous bone between the body element of the prosthesis and thecortical bone. This is because the cancellous bone is significantly moremetabolically active than the cortical bone and, as such, able to morequickly establish bone ingrowth with the prosthesis and remodel so as tocarry the load. The body element should also fill the inner canal of thebone to a large extent so as to help resist torsional loads placed uponit.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide animproved configuration for the body element of a modular prostheticfemoral stem component.

Another object of the present invention is to provide an improvedmodular prosthetic femoral stem component.

And another object of the present invention is to provide an improvedprosthetic total hip joint.

Still another object of the present invention is to provide an improvedmethod for restoring a hip joint.

These and other objects are addressed by the provision and use of thepresent invention.

In one form of the invention, there is provided an improved body elementfor use in a modular prosthetic stem component of the sort comprising abody element and at least one other element, wherein the body elementand the at least one other element are joined together by at least onemodular connection, wherein the improved body element comprises ananterior wall and a posterior wall, at least one of the anterior walland the posterior wall converging toward the other on the medial side ofthe body element and diverging away from the other on the lateral sideof the body element, whereby the body element approximates a generalwedge shape.

In another form of the invention, there is provided an improved modularprosthetic stem component comprising a body element and at least oneother element, wherein the body element and the at least one otherelement are joined together by at least one modular connection; andfurther wherein the body element comprises an anterior wall and aposterior wall, at least one of the anterior wall and the posterior wallconverging toward the other on the medial side of the body element anddiverging away from the other on the lateral side of the body element,whereby the body element approximates a general wedge shape.

In another form of the invention, there is provided an improvedprosthetic total hip joint comprising a modular prosthetic stemcomponent and a prosthetic acetabular cup component, wherein the modularprosthetic stem component comprises a body element and at least oneother element, wherein the body element and the at least one otherelement are joined together by at least one modular connection; andfurther wherein the body element comprises an anterior wall and aposterior wall, at least one of the anterior wall and the posterior wallconverging toward the other on the medial side of the body element anddiverging away from the other on the lateral side of the body element,whereby the body element approximates a general wedge shape.

In another form of the invention, there is provided an improved methodfor restoring a hip joint, the method comprising providing an improvedprosthetic total hip joint comprising a modular prosthetic stemcomponent and a prosthetic acetabular cup component, wherein the modularprosthetic stem component comprises a body element and at least oneother element, wherein the body element and the at least one otherelement are joined together by at least one modular connection; andfurther wherein the body element comprises an anterior wall and aposterior wall, at least one of the anterior wall and the posterior wallconverging toward the other on the medial side of the body element anddiverging away from the other on the lateral side of the body element,whereby the body element approximates a general wedge shape; anddeploying the improved prosthetic total hip joint in the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which are tobe considered together with the accompanying drawings wherein likenumbers refer to like parts and further wherein:

FIG. 1 is a schematic side view of a prosthetic total hip joint using amodular prosthetic femoral stem component formed in accordance with thepresent invention;

FIG. 2 is a schematic view of the proximal end of a femur prior toresection;

FIG. 3 is a schematic sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a schematic sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a schematic sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is a schematic top plan view of a body element formed inaccordance with the present invention;

FIG. 7 is a schematic sectional view taken along line 7-7 of FIG. 1;

FIG. 8 is a schematic sectional view taken along line 8-8 of FIG. 1;

FIG. 9 is a schematic sectional view taken along line 9-9 of FIG. 1;

FIG. 10 is a schematic top plan view of an alternative form of bodyelement also formed in accordance with the present invention;

FIG. 11 is a schematic sectional view like that of FIG. 7, exceptincorporating the alternative form of body element shown in FIG. 10;

FIG. 12 is a schematic sectional view like that of FIG. 8, exceptincorporating the alternative form of body element shown in FIG. 10;

FIG. 13 is a schematic sectional view like that of FIG. 9, exceptincorporating the alternative form of body element shown in FIG. 10; and

FIGS. 14-16 are schematic views of alternative forms of modularprosthetic femoral components utilizing the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Looking first at FIG. 1, there is shown a prosthetic total hip joint 5formed in accordance with the present invention. Prosthetic total hipjoint 5 generally comprises a modular prosthetic femoral stem component10 for seating in the proximal section of a resected femur 15, and aprosthetic acetabular cup component 20 for seating in the socket of theacetabulum 25.

Modular prosthetic femoral stem component 10 is formed in accordancewith the present invention. Modular prosthetic femoral stem component 10generally comprises a body element 30, a neck element 35 and a stemelement 40. Body element 30 includes a central aperture 45 into whichportions of neck element 35 and stem element 40 extend. As willhereinafter be discussed in further detail, body element 30 isconfigured and selected so that its outer surface 50 is appropriatelysized for proper seating in the proximal section of resected femur 15.Neck element 35 is selected so that when it is mounted to the remainderof modular prosthetic femoral stem component 10 and deployed withinfemur 15, the neck element's ball 55 will be properly seated in the hipjoint's corresponding acetabular cup 20. Stem element 40 is selected sothat its outer surface 60 is appropriately sized for proper seatingwithin the medullary canal of femur 15.

Body element 30, neck element 35 and stem element 40 are adapted to besecured to one another using a modular connection so as to form thecomplete prosthetic femoral stem component 10. Such modular connectionsare well known in the art.

In accordance with the present invention, body element 30 is configuredso as to transmit loads to the resected femur 15. To that end, bodyelement 30 has a profile which approximates, but is preferablyundersized relative to, the profile of the resected femur's corticalbone.

More particularly, and looking next at FIG. 2, there is shown theproximal end of a natural femur. As seen in FIGS. 3-5, the profile ofthe femur's cortical bone changes along the femur's length. It can beseen that the femur's anterior wall 70 is located at an angle withrespect to the femur's posterior wall 65, and that the femur's lateralaspect 75 and medial aspect 77 complete this general wedge shape.

Body element 30 is configured so that it closely approximates thisgeneral wedge shape. This is achieved by providing a body element whichhas an anterior wall and posterior wall, and wherein at least one of theanterior wall and posterior wall converges towards the other on themedial side of the body element and diverges away from the other on thelateral side of the body element.

Looking next at FIG. 6, in one preferred form of the invention, bodyelement 30 has an anterior wall 85, a posterior wall 80 and a lateralaspect 90 which together form a generally triangular configuration 95(FIG. 6), except that each of the vertices 100 preferably has a roundedconfiguration. In one preferred form of the invention, the generallytriangular configuration 95 preferably comprises an isosceles triangle,although it may also comprise any other sort of triangle, e.g., a righttriangle, an “irregular” triangle (i.e., a triangle with three differentvertex angles) or an equilateral triangle.

This general profile may contain cutouts, slots, grooves or the like aslong as the profile generally creates a shape which has threesubstantially flat sides, none of which are parallel to the others.Portions of the body may have the same or different triangular shape asvertically adjacent sections of the body, as need dictates.

As noted above, body element 30 is configured so that it closelyapproximates the general wedge shape of the femur's cortical bone.Preferably, however, body element 30 is slightly undersized relative tothe perimeter of the femur's cortical bone, such as is shown in FIGS.7-9. This construction permits a small amount of compacted cancellousbone 105 to be left between body element 30 and the femur's corticalbone. As noted above, the presence of this metabolically activecancellous bone facilitates bone ingrowth and bone remodeling.

It is also possible to form body element 30 with other configurations sothat it closely approximates the general wedge shape of the femur'scortical bone.

By way of example, it is possible to form the body element for a modularprosthetic femoral stem component with a generally trapezoidalconfiguration.

More particularly, and looking now at FIG. 10, body element 30A has ananterior wall 85A, a posterior wall 80A, a lateral aspect 90A and amedial aspect 92A which together form a generally trapezoidalconfiguration 95A, except that each of the vertices 100A preferably hasa rounded configuration.

This general profile may contain cutouts, slots, grooves or the like aslong as the profile generally creates a shape which has foursubstantially flat sides, only two of which (i.e., the lateral aspectand the medial aspect) are parallel to one another. Portions of the bodymay have the same or different trapezoidal shape as vertically adjacentsections of the body, as need dictates.

As noted above, body element 30A is configured so that it closelyapproximates the general wedge shape of the tibia's cortical bone.Preferably, however, body element 30A is slightly undersized relative tothe perimeter of the femur's cortical bone, such as is shown in FIGS.11-13. This construction permits a small amount of compacted cancellousbone 105 to be left between body element 30A and the femur's corticalbone. As noted above, the presence of this metabolically activecancellous bone facilitates bone ingrowth and bone remodeling.

In FIGS. 1-13, the improved configuration for the body element isdiscussed in the context of a so-called “three part” modular prostheticfemoral stem component. However, it should be appreciated that theimproved configuration for the body element can also be employed withother types of modular prosthetic femoral stem components, e.g., aso-called “two part” modular prosthetic femoral stem component such asis shown in FIG. 14 or FIG. 15; other types of “three part” modularprosthetic femoral stem components of the sort well known in the art; aso-called “four part” modular prosthetic femoral stem component such asis shown in FIG. 16; or other types of modular prosthetic femoral stemcomponents of the sort well known in the art.

It should, of course, be appreciated that various modifications may bemade to the preferred embodiments disclosed herein without departingfrom the scope of the present invention.

What is claimed is:
 1. A prosthetic total hip joint comprising: amodular prosthetic femoral stem component for seating in a proximalsection of a resected femur; and a prosthetic acetabular cup componentfor seating in a socket of an acetabulum; wherein said modularprosthetic femoral stem component comprises a body element, a neckelement, and a stem element; wherein said body element consists of foursubstantially flat sides comprising an anterior wall, a posterior wall,a lateral aspect, and a medial aspect, which are configured so as toform a generally trapezoidal configuration comprising four vertices,with said lateral aspect and said medial aspect being generally parallelto one another, and with the anterior wall and the posterior walltapering towards one another in the medial direction, so as to providerotational stability within the resected femur; and wherein each of thefour vertices of said body element is provided with a roundednon-angular configuration; said body element being sized and configuredto closely approximate the inner contour of the hard cortical bone ofthe resected femur while leaving a small amount of compacted cancellousbone between the body element and the cortical bone of the resectedfemur, such that said body element is adapted to fit in the resectedfemur; said body element being provided with an aperture into which aportion of said neck element and said stem element extend; wherein saidbody element and said stem element are joined together by a modularconnection; said stem element being of a size and configuration forseating within a medullary canal of the femur; wherein said body elementand said neck element are joined together by a second modularconnection; wherein said neck element is provided with a ball portionfixed thereon and adapted for seating in said acetabular cup; said bodyelement, said neck element, and said stem element being adapted to besecured to one another to form said prosthetic femoral stem component.